the Head in Ormthosaurs. 33 



wards birds in the plan of their pterygoid and palatine bones, 

 though there is nothing so typically bird-like in their form, 

 arrangement, and proportions as in the Cycnorhamphus. 



Another point necessary to a knowledge of the skull is the 

 composition of the lower jaw. And although only the dentary 

 and articular ends are known in the specimens from the Cam- 

 bridge Greensand, I propose to examine how much they really 

 make known. First, there is the dentary bone, which never 

 shows any indication of being composite : although numerous 

 specimens have been examined, there is never the slightest 

 trace of a median suture. The bone, in the only example 

 which is at all perfect*, has the palatal surface much longer 

 from back to front than the inferior surface, the dentary bone 

 being comparatively small, not extending further back than 

 do the teeth, and being undcrlapped throughout the greater 

 part of its short length by other elements of the lower jaw. 

 There is no direct evidence whether any of the Greensand 

 species had the bone prolonged backward beyond the sym- 

 physis. 



The largest fragment of the articular end at present known 

 (Woodwardian Museum, J. C. 12. no. 1) has been figured by 

 Prof. Owen in his Monograph on Pt. simus, published by 

 the Palseontographical Society, 1860. It is broken in front, 

 and shows on the upper part of the inner surface an area 

 from which a bone has come away. This bone, which did 

 not reach up to the superior border of the jaw, I think 

 may have been a backward process of the dentary element. 

 From front to back the exterior surface of this portion of 

 the jaw is convex, and the interior surface concave (as much 

 so as is usual among water-birds), suggestive of a median 

 approximation. Another and small fragment (Woodwardian 

 Museum, J. c. 12. no. 4) exhibits another sutural sm-face, 

 which demonstrates that a straight suture, parallel to the 

 inferior margin, and looking obliquely outward and upward, 

 divided the lower angular bone from the upper surangular 

 bone : the angular bone is the broadest from side to side ; it 

 is flattened underneath ; and a concave channel runs along its 

 inner sm-face from behind forward ; the surangular bone is much 

 the deeper from above downward, especially on the exterior 

 surface, and some distance in front of the articulation it is 

 compressed from side to side ; so that while the limit of the 

 bones is only marked by a slight groove externally, internally 

 the strong projecting ridge of the angular bone gives the sur- 

 angular an appearance of being deeply excavated. This bone 



* Omithosauria, pi. 12. fig. 1, 

 Ann. & Mag. N. Hist. Ser. 4. Vol. vii. 3 



